page_title: Yeast assimilable nitrogen
section_title: Risk in adding too much
hierarchical_section_title: Yeast assimilable nitrogen / Nitrogen supplementation / Risk in adding too much
caption_attribution_description: Français&#160;: Aspect de colonnies de Brettanomyces bruxellensis sur gélose YPD (Yeast Peptone D-glucose) lors d'un dénombrement par la technique des gouttes.
context_page_description: Yeast assimilable nitrogen or YAN is the combination of Free Amino Nitrogen, ammonia and ammonium that is available for the wine yeast Saccharomyces cerevisiae to use during fermentation. Outside of the fermentable sugars glucose and fructose, nitrogen is the most important nutrient needed to carry out a successful fermentation that doesn't end prior to the intended point of dryness or sees the development of off-odors and related wine faults. To this extent winemakers will often supplement the available YAN resources with nitrogen additives such as diammonium phosphate.
  However, the addition of excessive amounts of nitrogen can also create a hazard as other organisms besides beneficial wine yeast can utilize the nutrients. These include spoilage organisms such as Brettanomyces, Acetobacter and Lactic acid bacteria from the Lactobacillus and Pediococcus genera. This is why many wineries will measure the YAN after harvest and crushing using one of several methods available today including the nitrogen by o-phthaldialdehyde assay which requires the use of a spectrometer or the Formol titration method.
context_section_description: Nitrogen supplements, particularly DAP, stimulates yeast reproduction and can greatly increase the biomass. This could have the consequence of speeding up the fermentation rate faster than what a winemaker may desire and will also increase the fermentation temperature due to the heat being generated by the yeast. The excess biomass can also create a scarcity of other yeast nutrients, such a vitamins and sterols, due to increase competition and may lead to the production of off-odors (such as hydrogen sulfide) and even stuck fermentations.
  Excessive levels of the amino acid arginine (greater than 400 mg/l), especially near the end of fermentation, can pose the risk increase the production of ethyl carbamate. This is because arginine gets broken down into urea which can be reabsorbed and utilized by yeast or metabolized into ammonia. However, urea also reacts with ethanol if it is not completely metabolized which coupled with long term exposure (as well as high temperatures) can lead to the production of the ester ethyl carbamate.
  However, the greatest risk of over supplementing a must is that excess nitrogen and other nutrients will be left behind after fermentation is complete. This can create microbial instability as spoilage organisms can use these excess nutrients.
caption: Brettanomyces is one spoilage organism that can take advantage of excess nitrogen supplementation left in the wine.
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